Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$160.95	6.492%	$171.3989	$171.40	$171.40	$171.40
Purchase #2	$222.96	3.235%	$230.1728	$230.17	$230.15	$230.20
Purchase #3	$85.45	7.316%	$91.7015	$91.70	$91.70	$91.70
Purchase #4	$241.66	3.438%	$249.9683	$249.97	$249.95	$250.00
Purchase #5	$18.79	10.497%	$20.7624	$20.76	$20.75	$20.80
Purchase #6	$213.25	13.231%	$241.4651	$241.47	$241.45	$241.50
Purchase #7	$86.32	4.381%	$90.1017	$90.10	$90.10	$90.10
7 purchase totals =	$1,029.38		$1,095.5707	$1,095.57	$1,095.50	$1,095.70